Lecture 4 Flashcards
Random error:
Due to chance e.g. individual biological variation, sampling error, measurement error
Systematic error:
Due to bias e.g. selection bias and measurement bias
Better than random error because you can work with it/find reason for
How to avoid error?
Standardisation, larger sample size, blind/double blind, calibration of equipment
Confounding:
Error due to the introduction of an external factor that may skew the data and demonstrate a non-existent event
Solutions = randomization, restriction & matching *
Reliability:
The degree to which a test is consistent and stable * in measuring what it is intended to measure
Validity:
The degree to which the test actually measures what it claims to measure
Obesity in adults ages 20-50yrs…
35% overweight, 21% obese*
Males (64%) were more likely to be overweight or obese than females (49%)
Australia’s future ‘fat bomb’…
72% of middle-aged males and 58% of middle-aged females are overweight or obese
approx. 1.5 million Australians are obese
estimated 700,000 will be hospitalized and 122,500 men and women will die of obesity related CVD within next 20yrs
conservative costing of $3 billion extra in health expenditure *
Body frame size is a way to…
Evaluate “normalcy” of body weight with standardized charts
Body frame size measurements:
Stature measured in cm
Biacromial diameter 9cm): distance b/w most lateral projection of the acromial processes
Bitochanteric diameter 9cm): distance b/w most lateral projection of greater trochanters
Body frame size limitations:
Data derived primarily from white populations *
Provide no assessment of body comp
Overweight:
A body weight that exceeds some avg for stature, and perhaps age, usually by some SD unit or % (frequently accompanies and increase in body fat, but not always)
Overfatness:
When body fat exceeds and age and/or gender appropriate avg by a predetermine amount
Obesity:
The overfat condition that accompanies a constellation of comorbidities
BMI =
Body mass (kg) / height (m squared)
BMI underweight =
<18.5 km/m2
BMI normal =
18.5-24.9
BMI overweight=
25.0-29.9
BMI obesity I =
30-34.9
BMI obesity II =
35-39.9
BMI obesity III
> /40
Problem w/ BMI =
Assumes r/ship b/w BMI and % body fat remains independent of age, gender, ethnicity & race
Doesn’t consider the body’s proportional composition or fat distribution
Factors other than excess body fat affect the numerator of the BMI equation
The possibility of misclassifying someone as overweight pertains particularly to athletes
Human body comp component model:
Two: fat mass, fat-free mass
Three: water, protein, fat
Four: water, protein, bone mineral, fat
Methods to assess body comp – direct measurement
person dead
- dissolve body in chemical solution to determine fat and fat-free components
- physically dissect fat, fat-free adipose tissue, muscle, bone
Methods to assess body comp – indirect estimation
- hydrostatic weight using Archimedes’ principle
- skinfole thickness & girth measurements
- x-ray and MRI
- totally body electrical conductivity or bioimpedance
- near-infrared interactance
- ultrasound
Molecular techniques body comp
From body fluids -> isotopic dilution
Dual frequency energy x-ray absorptiometry (DEXA/DXA scam)
High cost, noninvasive, quick, gold standard
Body comp - tissue and organ level
-contains 11 systems
-this level groups 4 tissue systems to represent the total body mass
adipose tissue + skeletal muscle + bone + blood
MRI ultrasound
Body comp – whole body level
Anthrompometric measures – skinfolds, girths, bone diameters, segment lengths, body mass, stature
Segmental and totally body volume
Densitometry -> body density
2 component model - The density of fat is…
0.901g/cc (cubic cm) *
2 component model - The density of FFM…
is 1.10g/cc*
2 component model – the densities of fat and FFM componets….
(water, protein, mineral) are the same for all individuals
2 component model – the densities of tissues comprising the FFM are…
constant within an individual, and their proportional contribution to the LBM component remains constant
2 component model – the individual being measured differs from thereference body only….
In the amount of fat. The FFM of the reference body is assumed to be 73.8% water *, 19.4% protein , and 6.8% mineral
Siri equation:
Percentage body fat = (495 / body density) – 450
Siri equation assumes:
-two component model of body comp
limitations of density assumptions:
-values represent avgs, although they vary for populations, racial differences
Hydrostatic weighing:
when a body immersed in water, it’s buoyed by a counter force equal to the weight of the water displaced
-loss of weight in water, corrected for water density allows for calculation of body volume
take into account air in lungs
Bod pod:
Subject immersed in a closed air-filled chamber
r/ship of pressure vs volume, at a fixed temp, is used to solve for the volume of the subject chamber
Bioelectrical impedance analysis:
-measures resistance to electric current to predict body water content, lean body mass, and body fat
-current flows more rapidly through hydrated fat-free body tissue and water than through fat and bone
lower electrical resistance due to greater electrolyte content *
high practicality (fast, noninvasive measure)
affected by hydration*
Skinfold measurement:
Sum of skin fold is a good measure of subcutaneous adipose tissue
Can be used to estimate totally body fatness
Sum is inversely related to total body mass density and directly related to %BF
Skinfold measurement error…
Standardized procedures will increase the accuracy and precision of measurements
Skinfold measurement sites *
Triceps, subscapular, iliac, abdominal, thigh, chest, biceps
Triceps SKF
Vertical fold at posterior midline of right upper arm, halfway b/w tip of shoulder and tip of elbow
Subscapular SKF
Oblique fold, below right scapula’s lower tip
Iliac SKF
Slightly oblique fold, just above the right hipbone (crest of ileum); the fole follows the natural diagonal line
Abdominal SKF
Vertical fold 1 inch to the right of umbilicus
Thigh SKF
Vertical fold at the midline of right thigh, 2/3 the distance from the middle of the patella to the hip
Chest SKF
Diagonal fold on the anterior acillary line
Biceps SKF
Vertical fold at right upper arm’s midline
Girth measurement sites:
Right upper arm (biceps), right forearm< abdomen, buttocks, right thigh, right calf
Biceps girth site
Arm straight and extended in front of the body; measurement taken at midpoint b/w shoulder and elbow
Right forearm girth site
Max girth with arm extended in front of body
Abdomen girth site
1 inch above umbilicus
buttock girth site
max protrusion with heels together
right thigh girth site
upper thigh, just below buttocks
right calf girth site
widest girth midway b/w ankle and knee
